If the line is horizontal, it is the greek letter theta, often used to label an angle. If the line is diagonal, it is used to denote the diagonal of a circle. As the greek letter phi it is used to denote an empty set and also used to label an angle.
It means that if you do a simple question like 12-4 it equals 8 right? If you were using a label it could be a chocolate bar, donut or really anything. 8 donuts. :)
You label it square if it is a square
The 6th letter of the English alphabet or a failing grade in school.
Just label it with a symbol of your choice and that is its name! Some people prefer a lower case letter but that is not a necessity.
You can address it to Mr and Mrs. Smith. You could address it is as the Smith Family. Or you could address it as Mr. Smith and Family.
The A has no significance it is just to label that angle / point. You could use B or Z or & to label it as well. A is just often picked due to being the first letter of the alphabet.
Avery US Letter 5160
tag
1991
label named
Tag
astamp
Need an application for a diabled label
Tag
Irr.
The letter "B" is typically used to label the trough of a wave.